A skin biopsy is defined as sampling of the integumentary system for histologic evaluation and is a powerful diagnostic tool for the dermatologist. Although a biopsy may seem straightforward, its utility is enhanced when the clinician understands its applications and limitations. As with all diagnostic tools, the pretest probability that a patient will have a specific disease takes into account the prevalence of the disease and the clinical findings. A histological diagnosis should then be clinically correlated with the physician’s differential diagnosis. A skin biopsy is considered the gold standard for the diagnosis of skin lesions and requires that the clinician be familiar with certain key concepts.
The skin biopsy has several indications1:
Establishing or excluding a cutaneous diagnosis
Monitoring the evolution of a disease or treatment effects
Determining the extent of a skin tumor
Tissue sampling for culture (bacterial, fungal, or viral organisms)
Tissue for genetic or gene rearrangement evaluations (T-cell lymphomas)
Cosmetic removal of tissue
After the decision to perform a biopsy has been made, prior to obtaining consent, the type of biopsy and site selection with relevant photography should be performed. In addition, relevant medical history, anesthesia selection, and consideration of antibiotic prophylaxis should be reviewed.
SITE AND LESION SELECTION
The selection of a representative lesion takes into account the best site for diagnosis and cosmesis. When there is a single lesion, biopsy site selection is straightforward. If the disease process is more diffuse, as in exanthems, then proper site selection is important. There are anatomical locations that are more amenable to healing and less prone to scar development. In addition, there are areas that may be prone to a higher background of histological change, which could then obscure key histologic findings. Generally, it is best to avoid performing biopsies below the knee if possible because of the increased risk of infection and delayed wound healing. Sites overlying joints also have a poorer healing outcome and potential for worsened scarring. The back often heals with stretched scars and is a site in which wound care can be logistically difficult to perform.2 If possible, biopsy of the central face should be avoided for cosmetic reasons.
Of equal importance is selection of the lesion to be biopsied. Morphological appearance and the clinician’s suspicion of the pathology will guide the choice of where the biopsy should be performed. For a biopsy of a possible cancer, it is best to sample the entire growth. If this is not feasible, then the thickest portion of the tumor should be biopsied to best assess the depth of the neoplasm. For inflammatory disorders, the most recent lesion will generally be most diagnostic. This is especially true when a diagnosis of vasculitis is suspected. To improve diagnostic accuracy, it is important to avoid any necrotic, ...